Electrostatic recording devices utilizing dielectric webs in an array of electrodes, generally termed the recording styli, are well known. The principal of operation of main concern with respect to this invention is the creation of a latent electrostatic image on the dielectric web by means of raising individual stylus in the recording head to a sufficient electrical potential so as to ionize the air in the gap between the head and the dielectric web. Since the distance between the web and the recording styli is the most critical factor as to the amount of potential required for the ionization to take place, the maintenance of a constant distance remains a primary objective in the prior art.
The large majority of the prior art relating to the problem of bringing a recording head into proximity with a dielectric substrate relates to mechanical methods, sometimes augmented with electrical control so as to adjust the stylus. In some instances, the wear of the stylus is compensated by the movement of the web to be charged. Mechanical means to sense the distance between the stylus and the dielectric substrate are taught. Such prior art is represented by U.S. Pat. No. 2,850,350; U.S. Pat. No. 3,816,839; and U.S. Pat. No. 3,846,802. In all of this prior art, the problem of maintaining mechanical devices replaces the primary problem of the distance between the web and the dielectric surface.
In a different attempt to achieve a constant distance between the recording head and a dielectric web, there is taught the use of an air bearing or fluid cushion in U.S. Pat. No. 4,124,854. According to this patent, the recording head is provided with a chamber having outlets adjacent the recording styli. Compressed air is fed to the chamber and permits the head to float upon the compressed air released through the outlets. The dielectric web is maintained at a constant location by passing it over a fixed support. By utilizing an electrically conductive support, a ground element for the electrical circuit is also provided. While this approach greatly simplifies the solution of the problem, there remains the problem of the lateral consistency of the distance between the dielectric web and the multiple styli head across the entire width of the head and dielectric sheet.